A teat cup for a milking machine is an annular rigid shell with a port for attachment to a pulsating pressure line, as described generally in D. O. Noorlander, U.S. Pat. No. 3,096,740 and also as shown in T. W. Erbach, U.S. Pat. No. 4,269,143.
An elongated, resilient, tubular liner, called an inflation, fits inside the cup. The inflation is longitudinally stretched and secured between the ends of the cup to provide a substantially airtight chamber between the outside of the inflation and the inside of the cup. The port communicates with the chamber. A tubular part of the inflation may project outwardly of the downstream end of the cup for attachment to a milking line which is subjected to a substantially constant sub-atmospheric pressure. The tubular part thereby communicates the sub-atmospheric pressure to the interior of the inflation, the upstream opening of the inflation being sealed off by insertion of a teat. A pulsating vacuum line connected to the port communicating with the chamber carries a pressure which alternates between a higher pressure, typically atmospheric, and a lower pressure which will generally not be greater than the constant sub-atmospheric pressure applied to the vacuum milking line. When the higher pressure is applied to the airtight chamber there is an over-pressure on the exterior of the inflation. The inflation collapses, at least partially, in response to the overpressure.
The upstream end of the inflation may be a retaining skirt which is constructed to stretch fit over the upstream end of the cup to provide an airtight seal, as disclosed in U.S. Pat. No. 3,096,740, Near the downstream end of the inflation are one or more external integral annular ribs which are larger in diameter than the internal diameter of the downstream end of the teat cup. Accordingly the inflation is stretched axially between the upstream and downstream ends of the teat cup, and the annular rib is tensioned against the teat cup lower end to provide an airtight seal. Extending inward from the skirt is a resilient annular flange portion for receiving the teat and holding it during the milking operation.
Such annular flange is disclosed in U.S. Pat. No. 3,096,740 and also in J. Maier, U.S. Pat. No. 4,141,319. As disclosed in those patents, the inner periphery of the annular flange bends downward to receive the teat and hold it in the teat cup, with the intention of providing a milking movement in response to the periodic pressure changes produced by the pulsating vacuum. The annular flange is, for this purpose, made to be very flexible, as disclosed in D. F. Siddal, U.S. Pat. No. 3,474,760, in connection with an inflation of unitary construction.
In U.S. Pat. No. 3,096,740 an integrally formed external annular rib is provided around the exterior of the inflation, axially located in the middle section. A resilient sleeve surrounds the part of the inflation above the rib. The sleeve is intended to provide tension when a teat is inserted into the inflation, in order to grip the teat.
Known inflations have a number of drawbacks, including inadequate retention on the teat, uncomfortable and dangerous irritation and injury to the teat and udder, and short useful lifetimes due to wear and breakage.
Heretofore, tightly fitting inflations with correspondingly good retention characteristics caused the greatest teat irritation and injury, as a result of the tightness of the fit. A need therefore exists for an inflation which will hold securely to the teat during milking without causing irritation or injury either during milking or upon removal of the inflation. Inflations previously constructed from rubber have had lifetimes of the order of a thousand or so milkings. The rubber sleeve in U.S. Pat. No. 3,096,740, for example, had to be shielded by the inflation from the milk in the inflation in order to preserve the sleeve's elasticity. More recently, with the advent of silicone inflations, the lifetime has increased by a factor of about five. Nevertheless, it would be highly desirable to yet further increase the durability and hence the average lifetimes of silicone inflations by optimizing their design.